The present invention relates to a one-component RTV silicone rubber composition, and more particularly, the present invention relates to an alkoxy-functional one-component RTV silicone rubber composition having therein amine-functional scavengers.
One-component room-temperature vulcanizable silicone rubber compositions are well known. Such compositions disclosed in BRUNER, U.S. Pat. No. 3,035,016 and CEYZERIAT, U.S. Pat. No. 3,133,891. These patents disclose acyloxy-functional one-component RTV (RTV in this application refers to room-temperature vulcanizable) silicone rubber compositions. By acyloxy-functional, it is meant that the cross-linking agent in the composition was an acyloxy-functional silane and more particularly, an acetoxy-functional silane such as methyltriacetoxy-silane. The composition is prepared by mixing in an anhydrous manner, a silanol-terminated diorganopolysiloxane polymer with the acyloxy-functional cross-linking agent and a metal condensation catalyst. The resulting mixture was then compounded with fillers and various other ingredients in a substantially anhydrous manner. When it was desired to cure the composition, the composition was exposed to atmospheric moisture wherein the acyloxy groups hydrolyzed to cross-link the polymer to form a silicone elastomer. Since the early times of the BRUNER, U.S. Pat. No. 3,035,016 composition there have been devised various other types of functional RTV compositions such as ketoxime-functional RTV compositions, amine-functional RTV compositions, alkoxy-functional RTV compositions and so forth. An example of an amine-functional one-component RTV silicone rubber composition is to be found, for instance, in NITZSCHE, et al, U.S. Pat. No. 3,032,528. This patent utilizes an amine-functional silane as a cross-linking agent and has the advantages that it is fast-curing and non-corrosive. Nevertheless, it does give off an objectionable odor upon curing and sometimes toxic by-products.
One of the most advantageous types of one-component RTV compositions was the alkoxy-functional RTV composition. An example of such a composition is to be found in BEERS, U.S. Pat. No. 4,100,129. Such a composition gives off an alcohol by-product upon curing and as a result is substantially non-corrosive. Further, it does not give off objectionable odors upon curing and has many other advantageous properties. However, one of the disadvantages of the BEERS, U.S. Pat. No. 4,100,129 composition was the fact that it was not as shelf-stable as would be desired. That is, after prolonged storage of 6 months or more, it was found that the cure rate of the composition would be unnecessarily retarded. Various means were devised to preserve the shelf-stability of such a composition. However, all such means were not as successful as would be desired and necessitated additional steps in the preparation of the composition which increased the cost thereof. Another disadvantage of the BEERS, U.S. Pat. No. 4,100,129 composition is it did not have as rapid a cure rate as would be desired. This was true even with the titanium chelate catalysts of the BEERS patent. Accordingly, it was highly desirable to develop an alkoxy-functional RTV composition; that is, a composition that would cure through the hydrolysis and cross-linking of alkoxy-groups in the base polymer and which composition would be shelf-stable and have a rapid cure rate. It is hypothesized and has been hypothesized that the reason the BEERS, U.S. Pat. No. 4,100,129 composition does not have a sufficiently rapid cure rate and is not shelf-stable, was the fact that even though the composition was prepared anhydrously or in a substantially anhydrous manner, there became incorporated in the composition various unbonded hydroxy groups. Such unbonded hydroxy groups entered the composition as a result of their presence in the base silanol-terminated diorganopolysiloxane polymer or in the filler or in the various ingredients that were added to the composition. It was postulated that as a result of the unbonded hydroxy groups in such compositions, such hydroxy groups hydrolyzed the alkoxy groups to convert them to hydroxy groups. As a result, when the composition was exposed to atmospheric moisture it would cure slowly sometimes and other times it might not even cure at all; as a result of the converted hydroxy groups not being able to react and cross-link with each other. It has been postulated that the longer the polymer was packaged and maintained prior to exposure to atmospheric moisture for the purpose of curing it, the more alkoxy-groups would be hydrolyzed by the unbonded hydroxy groups and the more the shelf-stability and the cure rate of the composition would degrade. A recent development in rectifying this phenomenon is to be found in the disclosure of WHITE, et al, Ser. No. 277,524, filed on June 16, 1981, now U.S. Pat. No. 4,395,526 which discloses the use of scavengers and integrated cross-linker, scavengers for the purpose of reacting with unbonded hydroxy groups in the uncured RTV composition so as to preserve the shelf-stability and the cure rate of the RTV composition. Thus, it is disclosed in the foregoing WHITE, et al case, that there can be utilized in the composition a compound having a scavenging leaving group which is capable of readily and rapidly reacting with all unbonded hydroxy groups in the composition so as to render them useless or inactive for reacting with the alkoxy-groups in the base diorganopolysiloxane polymer. It is indicated in the WHITE, et al, case that such scavenging leaving groups can be either a pure scavenging compound or they can be present an integrated cross-linker, scavenger; that is, an integrated cross-linker, scavenger being one which has scavenging groups in it and also has alkoxy groups in it. Such a compound can react with the base silanol-terminated polymer to result in a polymer system or base polymer system having scavenging groups as well as having alkoxy-groups on the terminal silicon atoms of the base diorganopolysiloxane polymer. Accordingly, such end-cappers or integrated cross-linker, scavengers could be utilized to both end-cap the silanol-terminated polymer so as to produce a base polymer capable of cross-linking to form an RTV silicone rubber composition and also could be utilized to react with unbonded hydroxy groups in the composition so as to prevent such unbonded hydroxy groups from attacking and hydrolyzing the alkoxy groups in the system. It is indicated in the WHITE, et al, case that the scavenging leaving group can be an amine-functional group, both in the pure scavenger or in the integrated cross-linker, scavenger compound. Examples of such amine-functional scavengers and integrated cross-linker scavengers are given on page 21 of WHITE, et al, U.S. Pat. No. 4,395,526; such as, for instance, methyldimethoxymethylaminosilane, etc. It is disclosed in that patent, basically, that the integrated cross-linker, scavenger or pure scavenging compound has in the amine-functional group a single amine functionality, which can be utilized for the purposes of the WHITE, et al case. It has now been found unexpectedly that compounds having additional amine functionalities, siloxane amine compounds, can be utilized as scavenging compounds and as integrated cross-linker, scavengers. Such compounds react with unbonded hydroxy groups in the composition so as to preserve the shelf-stability and the cure rate of the alkoxy-functional RTV silicone rubber compositions. Such amine-functional compounds as disclosed by the instant case can be used as both pure scavengers or as integrated cross-linker, scavengers for the purpose of end-capping silanol terminated polymers to form the base polymer of an alkoxy-functional one-component RTV system having a rapid cure rate and good shelf-stability.
It is one object of the present invention to provide for an alkoxy-functional RTV composition having good shelf-stability in which there is present an amine-functional scavenging compound.
It is an additional object of the present invention to provide an alkoxy-functional one-component RTV silicone rubber composition having a rapid cure rate in which there is present a scavenging compound having an amine functionality for reacting with unbonded hydroxy groups.
It is yet an additional object of the present invention to provide for scavenging compounds and integrated cross-linker, scavenging compounds for reacting and bonding with unbonded hydroxy groups in alkoxy-functional one-component RTV compositions in which in each hydrolyzable leaving group in the scavenging compound, there is more than one amine functionality.
It is yet still an additional object of the present invention to provide a process for producing a shelf-stable, rapid-cure-rate one-component alkoxy-functional RTV composition in which there is present a scavenging compound or integrated cross-linker, scavenger compound having as a scavenging group an amine-functional group with more than one amine functionality in each such leaving group. These and other objects accomplished by means of the disclosure set forth herein below.